Sample injection in gas chromatography

ABSTRACT

Sample injection in gas chromatography is accomplished by passing a sample stream separate from the carrier gas stream and diverting it into the carrier gas stream through an unrestricted limb by adjusting the relative pressures of the two streams.

0 United States Patent [151 3,668,834 Deans [4 1 June 13, 1972 SAMPLE INJECTION IN GAS CHROMATOGRAPHY [56] References Cited [72] Inventor: David Robert Deans, Stockton-on-Tees, UNITED STATES PATENTS England 3,030,798 4/1962 Lichtentels ..55/ 197 X [73] Asslgnee: Imperial Chemical Industries Limited,

London England Primary Examiner-Jim L. DeCesare [22] F iled: July 31, 1970 Att0rneyCushman, Darby & Cushman [21] Appl. No.: 59,912 ABSTRACT [30] Ford n A cation Prior Data Sample injection in gas chromatography is accomplished by g pp y passing a sample stream separate from the carrier gas stream Aug. 14, 1969 Great Britain and diverting it into the carrier gas tream through an unrestricted limb by adjusting the relative pressures of the two U.S. streams [51] Int. Cl ..B0ld 15/08 [58] Field of Search ..55/67, 197, 386; 73/23.1 12 Claims, 2 Drawing Figures PATENTEDJUH 13 I972 SHEET 2 BF 2 SAMPLE INJECTION IN GAS CHROMATOGRAPHY This invention relates to sample injection in gas chromatography.

The injection of samples to be analyzed into carrier gas streams in gas chromatography has in the past been accomplished by injection through a septum with a hypodermic syringe or by using a variety of valves which may operate by injecting liquid or gas. If valves are used they have to operate at a variety of temperatures so that the gas or liquid introduced will be at a suitable temperature. This requirement introduces a difficulty, particularly where high temperatures are required, as the maximum temperature at which a valve can operate satisfactorily is limited by the design and material of construction. The use of a hypodermic syringe sufiers from the disadvantages that it requires a trained operator and the precision with which a repeatable volume can be injected is relatively poor. This method also, in repeated use, leads to leaking of the septum and is not suitable for injecting samples I from a continuously flowing stream of liquid or gas.

According to this invention means for supplying a stream of carrier gas to one ormore chromatographic columns and injecting a sample at will into the said stream comprises a junction from which the said chromatographic column or columns are fed, a pressure or flow controller connected to one limb of the junction for feeding the junction with carrier gas, a conduit for conveying a stream from a second pressure or lflow controller to a vent, an unrestricted sample injection limb between the junction and the conduit for feeding the sample to the junction and means for diverting a sample from the said conduit through the sample injection limb to the junction by creating an appropriate pressure difference along the sample injection limb.

The invention also provides a method of injecting sample into a chromatographic column which comprises passing a continuous stream of carrier gas through the column, passing a separate stream of a gas or liquid to be sampled and diverting part of the separate stream of gas or liquid to be sampled into the carrier gas stream through an unrestricted sample injection limb by varying the pressure difference across the said limb.

According to one form of the invention means for supplying a stream of carrier gas to one or more chromatographic columns and injecting a sample at will into the said stream comprises a junction from which the said chromatographic column or columns are fed, means which comprises a first pressure or flow controller for supplying the carrier gas to the junction through a carrier gas limb and a sample injection limb for feeding the sample to the junction, which limb leads from a conduit which is provided with (a) means for admitting gas to the conduit at a controlled rate of flow and (b) a vent which comprises a restriction to gas flow, the vent being closeable.

According to a further form of the invention means for supplying a stream of carrier gas to one or more chromatographic columns and injecting a sample at will into the said stream comprises a junction from which the said chromatographic column or columns are fed, means which comprises a first pressure or flow controller for supplying carrier gas to the junction through a carrier gas limb and a sample injection limb for feeding the sample to the junction, which limb leads from a conduit provided with (a) means for admitting gas to the conduit at a controlled pressure and (b) a vent which comprises a restriction to gas flow, either the vent or the carrier gas limb or both being closeable and if the vent only is closeable a restriction to gas flow is provided on the output side of the means for admitting gas to the conduit. If the sample passes through the latter restriction to gas flow it is preferably non absorbtive to the sample.

According to this invention, therefore, means for supplying a stream of carrier gas to one or more chromatographic columns and injecting a sample at will into the said stream comprises a junction from which the said chromatographic column or columns are fed, a first controller of pressure or flow for feeding carrier gas to the junction and a sample injection limb for feeding the sample to the junction, leading from a conduit which is provided with (a) means for admitting gas to the conduit at a controlled rate of flow or means to admit gas at a controlled pressure and (b) a vent which comprises a restriction to gas flow, either the vent or (providing the first controller is a pressure controller) the carrier gas limb or both being closeable, and, if the vent only is closeable and (a) is a means for admitting gas at a controlled pressure, a restriction to gas flow is provided on the output side of (a). If sample passes through the latter restriction it is preferably non absorbtive to the sample.

The apparatus is operated if the vent is closeable by passing the material to be sampled in a continuous gas stream flowing from the means for admitting gas to the conduit to the vent, if the means for admitting gas to the conduit is a pressure controller, setting it to operate at a higher output pressure than the first pressure or flow controller, setting the pressure in the sample injection limb at a value below that of the carrier gas when the vent is open and when it is desired to inject a sample closing or further restricting the vent. The pressure in the sample injection limb thus rises above that of the carrier gas and a sample from the continuous gas stream passes into the junction.

If the carrier gas limb only is closeable, a sample is injected by admitting gas to the conduit and closing the carrier gas limb. When corrosive materials are to be sampled, using this form of the invention, no means for closing the vent is required and the means for closing the carrier gas limb need not come into contact with the sample. As closing means are easily damaged by corrosive materials, this form of the invention offers a substantial advantage in this case.

If desired the continuous gas stream, i.e. sample flow may consist normally of carrier gas, and a sample to be an analyzed may be introduced into the carrier gas using for example a hypodermic syringe and septum. Closing and opening of the vent or carrier gas limb is then timed to take place as the sample passes the junction.

By closing the vent for a reproducible time a reproducible sample can be introduced. Preferably the vent is opened and closed by an automatic timer, which acts at an appropriate interval after the introduction of the sample to the continuous gas stream. The timer may if desired be set manually at the time of introduction of the sample to the continuous gas stream, or by the closure of electrical contacts on the hypodermic syringe.

All of the restrictions in the above device may be incorporated in an oven together with all necessary chromatographic columns. The sole adjustment necessary in order to inject the sample involves temporarily closing the vent or the carrier gas limb or both and this may be performed by tap(s) situated outside the oven.

If the flow of carrier gas through the junction is programmed a variable loss of carrier gas will take place through the closeable vent but this can be accommodated if desired by an appropriate adjustment to the carrier gas program or alternatively by programming the second flow controller by the same program as the first controller. If the carrier gas pressure is programmed, and a second pressure controller and restriction to gas fiow is used to feed the conduit, the same object may be attained by programming the second controller by the same programmer as the first. If it is desired to program the pressure of carrier gas applied to the junction it may be desirable to program the pressure applied by the second controller in order to ensure that it always operates at a pressure higher than that of the first controller though if the pressure is set at a value such that it exceeds that of the first controller at all times when it is desired to introduce a sample this is unnecessary.

If desired the sample injection limb or the conduit for conveying the sample flow may be provided with a second vent controlled by a restriction only; this enables any desired proportion of the sample flow to be bled off. This confers greater stability during the injection cycle.

Unused sample may be returned to any process which is being monitored.

One form of the invention will now be described with reference to the accompanying drawing in FIG. 1 which shows an apparatus according to the invention in diagrammatic form. A pressure controller 1 feeds a junction 2 which in turn feeds a chromatographic column 3, which leads to a flame ionization detector 4 which vents to the atmosphere. A second limb 6 feeding the junction 2 is provided with an inert arm leading from a constant flow controller 7 through a liquid sample injection vaporizer (Le. a sample injection preheater) 8, which comprises a septum for injecting the sample by means of a hypodermic syringe, and a hot wire detector 9 which is electrically connected to a pulse generator 10. An outlet arm 11 leads from between the junction 2 and the hot wire detector 9 through a needle valve 12 and a solenoid operated on/off tap 13, which on/off tap is operated after a time delay by a timer 14 which is set on receipt of a pulse from the pulse generator 10, to close and open the tap 13 at a pre-set time interval. The inlet arm and outlet arm constitute the conduit for conveying the sample flow.

The apparatus is operated as follows.

The constant pressure controller 1 and the constant flow controller 7 are connected to a supply of carrier gas. The constant pressure controller 1 and needle valve 12 are set to provide a slightly higher pressure at the junction 2 than arises from the constant flow controller 7 when the tap 13 is opened. Under these conditions the flow from the constant flow controller 7 passes through the preheater 8, detector 9, the needle value 12 and the tap 13 to the atmosphere. The carrier gas from constant pressure controller 1 passes through the chromatographic column 3.

When a sample is injected by means of a hypodermic syringe into the vaporizer 8 a block of sample vapor passes to the hot wire detector 9 and as the front of this block passes through the hot wire detector the resistance of the wire is altered as the rate of heat lost in the sample atmosphere will differ from that obtaining in a carrier gas atmosphere. The change in resistance of the hot wire on entry of the sample to the detector generates a pulse in the pulse generator which sets the timer 14 to close the tap 13 after the sample reaches the limb 6. The pressure arising in the limb 6 thus increases and a portion of the sample passes to the junction 2 and from thence to the chromatographic column 3. After a pre-set interval the timer 14 opens tap 13 and the remainder of the sample is vented.

By this means a reproducible quantity of sample is introduced to the column at any given flow rate of the constant flow controller 7.

Instead of the hot wire detector 9 and pulse generator 10, the timer may be actuated, for example by the closure of contacts on a hypodermic syringe when the sample is injected.

Also, if desired the time delay may be built into the gas system by providing a branch in the line from the preheater 8 leading to a detector, omitting detector 9, and adjusting the dimensions such that sample reaches the detector just after it reaches the limb 6.

Another form of the invention will now be described with reference to F IG. 2 which is a diagrammatic representation of an apparatus according to the invention.

Differential pressure controllers and 21 supply carrier gas to the apparatus at a fixed relative pressure with respect to each other. Controller 20 feeds a liquid sample injection vaporizer 22 which in turn feeds conduit 23 from which sample injection limb 24 leads to a junction 25. Conduit 23 vents to the atmosphere through a fixed restriction 26.

Controller 21 feeds a carrier gas inlet 27 to junction through an on/ofi" tap 28 which is operative after a time delay by a timer 29. A line 30 leads from junction 25 to a chromatographic column 31, the effluent from which passes to a flame ionization detector 32 which vents to the atmosphere.

A hypodermic syringe (not shown) of conventional design is electrically connected to the timer 29 so as to provide a signal by the closing of contacts in it when a sample is ejected from the hypodermic syringe.

The apparatus operates as follows:

Differential pressure controllers 20 and 21 are supplied with carrier gas and set at relative pressures such that the pressure in line 23 is approximately the same or slightly less than that at junction 25 when on/off tap 28 is open. A sample is injected by means of the hypodermic syringe into the sample injection vaporizer 22 providing a signal to timer 29 which is set to close on/off tap 28 as the vaporized sample is carried past limb 24 and to re-open tap 28 after a pre-determined interval. When tap 28 is closed the pressure at junction 25 drops below that in conduit 23 and part of the sample passes along limb 24 and into column 31. When the on/off tap 28 is re-opened no further flow of sample down limb 24 takes place and the sample is passed through column 31 and the effluent detected in the flame ionization detector 32.

I claim:

1. Apparatus for supplying a stream of carrier gas to a chromatographic column and injecting a sample into the said stream which comprises a junction from which the chromatographic column is fed, a gas controller connected to one limb of the junction for feeding the junction with carrier gas, a conduit for conveying a sample flow from a second gas controller to a vent, an unrestricted sample injection limb between the junction and the conduit for feeding a sample to the junction and means for diverting sample from the said conduit through the sample injection limb to the junction by creating an appropriate pressure difference along the sample injection limb.

2. Apparatus for supplying a stream of carrier gas to a chromatographic column as claimed in claim 1 in which the conduit is fed by a flow controller and the means for diverting the sample from the conduit through the sample injection limb to the junction comprises a restriction to gas flow in the vent from the conduit, and means for closing the vent.

3. Apparatus as claimed in claim 1 in which the conduit is fed by a pressure controller and the means for diverting sample from the conduit through the sample injection limb to the junction comprises a restriction to gas flow in the vent of the conduit, means for closing the vent and a restriction to gas flow on the output side of the pressure controller admitting gas to the conduit.

4. Apparatus as claimed in claim 1 in which the conduit is fed by a pressure controller and the means for diverting sample from the conduit through the sample injection limb to the junction comprises a restriction to gas flow in the vent of the conduit, a restriction to gas flow on the output side of the pressure controller admitting gas to the conduit, and means for closing the carrier gas limb.

5. Apparatus as claimed in claim 1 in which means is provided for introducing a sample into a continuous gas stream passing through the conduit before it reaches the junction.

6. Apparatus as claimed in claim 5 in which means is provided to pass sample through the sample injection limb at a pre-set time after the introduction of the sample.

7. Apparatus as claimed in claim 6 in which the timing means injects the sample for a pre-set period of time.

8. Apparatus as claimed in claim 1 in which both controllers are pressure controllers and they are linked to a common means for controlling their pressure setting.

9. Apparatus as claimed in claim 1 in which the conduit is provided with a second vent controlled by a restriction.

10. A method of injecting sample into a chromatographic column which comprises passing a continuous stream of carrier gas through the column, passing a separate stream of a fluid to be sampled and diverting parts of the separate stream of fluid to be sampled into the carrier gas stream through an unrestricted sample injection limb by varying a pressure difference across the limb.

ll. Chromatographic apparatus comprising: a chromatographic column; a first carrier gas controller for receiving carrier gas from a source thereof; a first conduit extending from the first gas controller to the column; a second carrier gas concarrier gas to and through the column; efi'ecting a separate stream of carrier gas; providing a connection between the streams; adding fluid to be sampled to the separate stream carrier gas; and then diverting parts of the separate stream through the connection into the continuous stream by varying the pressure in one of the streams so as to effect a negative pressure differential between the continuous stream and the separate stream. 

2. Apparatus for supplying a stream of carrier gas to a chromatographic column as claimed in claim 1 in which the conduit is fed by a flow controller and the means for diverting the sample from the conduit through the sample injection limb to the junction comprises a restriction to gas flow in the vent from the conduit, and means for closing the vent.
 3. Apparatus as claimed in claim 1 in which the conduit is fed by a pressure controller and the means for diverting sample from the conduit through the sample injection limb to the junction comprises a restriction to gas flow in the vent of the conduit, means for closing the vent and a restriction to gas flow on the output side of the pressure controller admitting gas to the conduit.
 4. Apparatus as claimed in claim 1 in which the conduit is fed by a pressure controller and the means for diverting sample from the conduit through the sample injection limb to the junction comprises a restriction to gas flow in the vent of the conduit, a restriction to gas flow on the output side of the pressure controller admitting gas to the conduit, and means for closing tHe carrier gas limb.
 5. Apparatus as claimed in claim 1 in which means is provided for introducing a sample into a continuous gas stream passing through the conduit before it reaches the junction.
 6. Apparatus as claimed in claim 5 in which means is provided to pass sample through the sample injection limb at a pre-set time after the introduction of the sample.
 7. Apparatus as claimed in claim 6 in which the timing means injects the sample for a pre-set period of time.
 8. Apparatus as claimed in claim 1 in which both controllers are pressure controllers and they are linked to a common means for controlling their pressure setting.
 9. Apparatus as claimed in claim 1 in which the conduit is provided with a second vent controlled by a restriction.
 10. A method of injecting sample into a chromatographic column which comprises passing a continuous stream of carrier gas through the column, passing a separate stream of a fluid to be sampled and diverting parts of the separate stream of fluid to be sampled into the carrier gas stream through an unrestricted sample injection limb by varying a pressure difference across the limb.
 11. Chromatographic apparatus comprising: a chromatographic column; a first carrier gas controller for receiving carrier gas from a source thereof; a first conduit extending from the first gas controller to the column; a second carrier gas controller for receiving carrier gas from a source thereof; a second conduit extending from the second gas controller to a vent; means for adding a sample to said second conduit; an unrestricted sample line connecting said second conduit with said first conduit; and adjustable restricting means in one of said conduits for diverting flow from said second conduit through said sample line into said first conduit by creating a pressure difference between the first and second conduits.
 12. A method of injecting sample into a chromatographic column which comprises: effecting a continuous stream of carrier gas to and through the column; effecting a separate stream of carrier gas; providing a connection between the streams; adding fluid to be sampled to the separate stream carrier gas; and then diverting parts of the separate stream through the connection into the continuous stream by varying the pressure in one of the streams so as to effect a negative pressure differential between the continuous stream and the separate stream. 